The present invention relates to an infrared radiation reflecting layer system on a transparent substrate having a sequence of layers that are applied to the substrate and reflect infrared radiation. The sequence of layers includes at least one selective function layer.
The invention also relates to a method for manufacturing such a layer system in which an infrared radiation reflecting layer sequence is applied to a transparent substrate by a suitable method.
In general, an infrared radiation reflecting layer system (low-E layer system) comprises the function layer, a base layer that improves adhesion of the function layer and a reflection reducing top layer, whereby the individual layers may repeat within the layer system. The function layer, usually consisting of a noble metal, mostly silver, or an alloy thereof, has a good selective reflectivity in the infrared range even with a small layer thickness. If only one function layer is arranged in the layer system, this is often referred to as a “single low-E” system.
The top layer also serves to improve the mechanical and chemical stability, in addition to reducing reflection. It is usually made of a highly refractive dielectric material containing silicon. To increase the transmittance of the layer system in the visible range, these reflection-reducing layers are arranged above and beneath the selective function layer.
Such infrared radiation reflecting transparent layer systems are also subjected to tempering processes to harden and/or shape the substrate. In this case they have a layer sequence having layer properties such that a substrate having this layer system may be subjected to a heat treatment and any changes that occur in the optical, mechanical and chemical properties of the layer system may be kept within defined limits. Depending on the application of a coated substrate, its layer system is exposed to different climate conditions in different time regimens during the tempering process.
Because of different thermal loads to which the layer sequences already applied are subjected, various processes that alter the reflectivity of the function layer and the transmittance of the layer system occur in the course of production of the following layers of the layer system and the tempering process, in particular diffusion of components of the reflection reducing layer into the function layer and vice versa. To prevent such diffusion processes, a blocking layer that serves as a buffer for the diffusing components is inserted between the reflection-reducing layer and the function layer. These blocking layers are structured and arranged according to the thermal burden that occurs and protect the sensitive function layer, which is often very thin or the function layers from the influence of neighboring layers. In particular shifts in color of the layer system and an increase in surface resistance of the layer system due to the tempering process are prevented by the introduction of one or more blocking layers.
In particular NiCr or NiCrOx layers are known as blocking layers for temporable layer systems. For example DE 035 43 178 and EP 1 174 379 describe blocking layers which include silver layer(s) or at least protect them on one side. However, the blocking layers cause a reduction in conductivity of the silver layer(s). If a silver layer with a surface resistance of approx. 5 ohm/sq. is deposited and embedded in two NiCrOx layers, this embedding may lead to an increase in the surface resistance by approx. 1.5 ohm/sq. to 6.5 ohm/sq. [sic].
EP 0 999 192 B1 describes a layer system including a silver layer as a selective function layer which is provided with a blocking layer of nickel or nickel chromium on both sides. By introducing an NiCrOx layer into the functional silver layer in a single low E system, the layer system is stabilized in the heat treatment. The disadvantage is that with this layer system, each individual layer of the two silver partial layers must be approximately 7 to 8 nm thick to prevent the formation of islands with the silver partial layers. This in turn leads to a low transmittance of the layer system. Furthermore, EP 0 999 192 B1 discloses the use of a substoichiometric TiOx layer between the blocking layer and the silver layer, which should reduce the so-called haze formation, i.e., the change in optical properties of the function layer due to diffusion processes into the function layer. However, this absorbent TiOx layer undergoes oxidation during the heat treatment, resulting in significant changes in the transmittance and a shift in the preset color locus.
EP 1 238 950 A2 discloses a temperable layer system that is provided with NiCrOx layers as blocking layers on both sides of a silver layer as the sensitive layer.
Furthermore, dielectric interface layers are provided in this layer system and are situated above and below the blocking layers. Such layers have various stabilizing effects on the layer system and also act as a diffusion barrier during the tempering processes.
Furthermore, EP 1 238 950 describes the use of gradient layers in stabilization of heat-treatable layer systems. The disadvantage here is that the SiNx layer is beneath the blocking layer so that the electric surface resistance and thus the emissivity of the layer system are not reduced. In this approach, several layer sequences of sensitive silver layers with underlayers and two blocking layers enclosing the respective silver layer are provided.
DE 100 46 810 also discloses the application of metallic blocking layers which form a gradient layer with the silver as the function layer in a transitional area between the two layers. The reflection-reducing layer may also consist of several metal oxide layers with a gradient layer consisting of two neighboring individual layers between them.
The use of metal oxides for the reflection reducing layer does not constitute an optimal approach so the reflection reducing layer in DE 101 31 932 consists of several individual layers of different metal nitrides, whereby the amount of material in a layer is reduced from initially 100% to 0% and the amount of material in the neighboring individual layer is increased from 0% to 100% to the same extent. However, it has been found that this layer system also fails to ensure the desired transmittance.
It has been found that these different layer structures are still too sensitive for climate changes and only special tempering processes are suitable despite the various measures employed, so that they cannot be manufactured in a satisfactory quality or yield when there are demanding or definitely different climate conditions.
These layer systems have quality problems in production, even in the case of raw glass in undefined starting states, i.e., a fluctuating chemical composition of the glass, in particular with regard to its sodium content. Furthermore, other glass influences such as corrosion or impressions of the section devices that are used in handling the glass and are often not detectable by visual inspections and cannot be eliminated by the usual cleaning operations, cause unwanted changes in the properties of the layer system. With such glass influences, it is a particular disadvantage that their effects on the properties of the layer system become visible only after the tempering process.